Microbial test standard for use in infrared spectrometry

Abstract

The invention relates to a microbial test standard for use in infrared spectrometry which has at least two resealable vessels which are liquid-tight when closed, each of which contains a predefined amount of dried biomass of a microorganism. The microorganisms in the different vessels differ in at least one characteristic, which is selected in particular from the group comprising species, subspecies, strain, serovar, pathovar, toxivar and variety, and the difference manifests itself in a predefined intermicrobial spectral distance. The disclosure furthermore comprises a method of using the microbial test standard.

The invention claimed is: 
     
       1. A method of evaluating a spectral specificity of an infrared (IR) spectrometric measurement, the method comprising:
 providing a microbial test standard having at least two resealable vessels which are liquid-tight when closed, each of which contains a predefined amount of dried biomass of a microorganism, wherein the microorganisms in the respective vessels differ in at least one characteristic that manifests itself in a predefined spectral distance between spectral signatures in infrared spectra of the respective biomasses; 
 combining each biomass with a solvent to produce first and second biomass suspensions; 
 applying a predetermined quantity of each suspension to a different sample spot of an infrared spectrometry sample support plate; 
 drying each of the suspensions on the sample support plate and acquiring infrared spectra of the sample on each sample spot; 
 measuring the spectral distances between spectral signatures of the infrared spectra acquired from the samples; and 
 comparing the measured spectral distances to the predefined spectral distance and identifying the measurement as meeting a satisfactory performance limit if said measured spectral distances are within a predetermined range relative to the predefined spectral distance. 
 
     
     
       2. The method according to  claim 1 , wherein the at least one characteristic is selected from the group: species, subspecies, strain, serovar, pathovar, toxivar and variety. 
     
     
       3. The method according to  claim 1 , wherein the dried biomass is comprised of vacuum-dried pellets. 
     
     
       4. The method according to  claim 1 , wherein the microorganisms belong to different strains of one bacterial species. 
     
     
       5. The method according to  claim 1 , wherein the vessels have screw caps. 
     
     
       6. A method of evaluating a validity of an infrared spectrometric measurement of samples on an infrared spectrometry sample support having an array of sample spots on which are deposited analytical samples with unknown infrared spectral properties, the method comprising:
 providing a microbial test standard having at least two resealable vessels which are liquid-tight when closed, each of which contains a predefined amount of dried biomass of a microorganism, wherein the microorganisms in the respective vessels differ in at least one characteristic that manifests itself in a predefined spectral distance between spectral signatures in infrared spectra of the respective biomasses; 
 combining each biomass with a solvent to produce first and second biomass suspensions, 
 applying a predetermined quantity of each of the first and second suspensions to a different one of the sample spots of the sample support and drying of the suspensions to form microbial test standard sample spots, 
 acquiring infrared spectra from the microbial test standard sample spots; 
 acquiring infrared spectra from the analytical sample spots; 
 measuring spectral distances between spectral signatures in the infrared spectra of the different microbial test standard sample spots; 
 comparing the measured spectral distances to the predefined spectral distance to determine whether said measured spectral distances are within a predetermined range relative to the predefined spectral distance; and 
 identifying infrared spectra from the analytical samples on the sample support as being invalid measurements if said measured spectral distances are not within said predetermined range. 
 
     
     
       7. The method according to  claim 6 , wherein the measured spectral distances are computed from the microbial spectral signatures in a predetermined wave number range and correspond to a predetermined distance. 
     
     
       8. The method according to  claim 7 , wherein the predetermined wave number range is between around 1,300 and 800 cm −1 . 
     
     
       9. The method according to  claim 6 , wherein the spectral distances between the spectral signatures of the infrared spectra of the different microbial test standard sample spots are computed to examine the spectral reproducibility. 
     
     
       10. The method according to  claim 9 , wherein the predetermined range extends to a maximum distance A, which is a measure for the reproducibility of the acquired infrared spectra, and extends from a minimum distance B, which is a measure of spectral specificity in the acquisitions. 
     
     
       11. The method according to  claim 6 , wherein the solvent for the re-suspension contains distilled and/or deionized water. 
     
     
       12. The method according to  claim 6 , wherein each biomass is combined with the solvent in its respective vessel, and wherein the method further comprises mixing each biomass with the solvent by agitating the vessels or by mix-pipetting. 
     
     
       13. The method according to  claim 6 , wherein a plurality of replicates of the microorganism suspensions are applied to the sample support. 
     
     
       14. The method according to  claim 1 , wherein the dried biomass is sterilized. 
     
     
       15. The method according to  claim 1 , wherein the microorganisms are taken from the species  Escherichia coli  and the dried biomass in the different vessels comprises the strains DH5a (DSM 6897) and ML3 (DSM 1058).